PS: Since you are going to all the trouble of recoating the tub, at the same time be sure to buy a new "stop and waste" set for the drain at the end of the tub and the stopper mechanism. These used to be quite spendy, but now they come in very inexpensive (and corrosion-proof) black ABS plastic for the hidden parts with stainless-steel or chrome-on-brass for the exposed parts. (REALLY cheap ones will use chrome on zinc or pot metal--not worth the small savings.) I prefer the kind where either the stopper rises and seals with a lever in the overflow opening, or where the stopper is fully concealed in the back-of-tub overflow pipe so there is no exposed stopper to step on.

Follow the instructions packed with the model you choose and seal between part and tub with a wipe of Silicone caulking before tightening. Leave what squeezes out alone until it has set up for 10 minutes or so, then carefully wipe off excess. (It will be smeary if wiped too soon and very hard to get off if left until fully cured overnight.) Choose the silicone marked "TUB AND BATH", since it is treated not to stain or mildew when around water.

This is only the beginning, you know. Once you get your tub jazzed up and add a shiny stop and waste, the tub surround will suddenly look very shabby. When you replace that, you will notice how tacky the faucets and shower head now appear, and then....you get the idea...